1. Field of the Invention
The present invention relates to an improved device for fixing in place a prosthetic device in the human mouth and a method for producing the same.
2. Description of Related Art
A superior dental adhesive product has been commercially available under the trademark SEA-BOND.RTM. and is used in the human mouth to bond a denture to the soft gum tissues. As described in U.S. Pat. No. 4,503,116, the disclosure of which is incorporated herein by reference, the dental adhesive is a laminate of webs having a carrier portion with fibers thermoplastically bonded together by an interposed layer of ethylene oxide polymer powder. The ethylene oxide polymer powder is a dry, water-activated adhesive.
Accordingly, the plastic properties of the ethylene oxide polymer make a better laminate and its water-activated adhesive properties improve the laminate denture fixability. Such fixative properties are further improved by admixing another dry, water-activated adhesive material, such as sodium alginate, with the ethylene oxide polymer powder to promote formation of a gel-like adhesive mass between the denture plate and the mouth tissue.
To prepare the dental adhesive product, a fiber-faced web is formed by arranging a layer of loose synthetic fibers on a carrier such as a cellulosic paper. The loose fibers are passed through the carrier by needle-punching them so the fibers protrude from either side of the paper. A pair of such fiber-faced carriers are heat- and pressure-bonded together by the thermoplastic powder layer, such as ethylene oxide polymer powder to which a dry powder fixative, such as sodium alginate, has been added.
In the product of U.S. Pat. No. 4,503,116 as illustrated in FIG. 1, a pair of fiber-faced webs 10, 12 are formed and rolled into feed rolls 14, 16. One web roll is fed under an electrostatic powder spreader 18, which progressively applies a bonding agent 20 of powdered ethylene oxide polymer to the facing surface of web 10. The other web 12 is fed to be superimposed above and in contact with web 10 via idler roll 21 so the bonding agent 20 is spaced therebetween. The resulting web and powder sandwich 22 is fed into a nip of a pair of heated calendar rolls 24, 26 which are sufficiently heated to melt the powdered thermoplastic bonding agent in order to bond the web fibers into a unitary laminate 28 which is typically rolled up onto a core 30.
While the resulting product has enjoyed great commercial success, further improvements are desired.
When the powdered ethylene oxide is dispersed as a powder shower 20 from powder spreader 18, such as an Oxy-Dry electrostatic powder spreader, onto the fiber-faced web, certain nonuniformities in the dispersed powder sometimes occur. The powder can be dispersed to form a nonuniform powder layer with varying thickness across the web. This can affect the strength of the thermoplastic bond which is formed thereafter. Occasionally, the powder is dispersed as large agglomerates or clumps 19, which prevent complete fusion of webs 10 and 12 and rejection of the resulting laminate. Where the powder layer is of nonuniform thickness and/or clumps of powder are present, the resulting product produced contains portions which are not useable.
In addition, powder fines are present or are formed by handling commercially available ethylene oxide powder, such as polyox WSR-301 brand ethylene oxide polymer. When such powder is dispersed on the web, fines are released to create dust problems. The resulting polymer dust must be collected and/or eliminated from the manufacturing operation. The dust which is so removed is wasted to the process and its removal increases equipment needs, the energy cost and monitoring costs.
Moreover, the step of depositing a uniform layer of powder on a fiber-faced web is slower than the other manufacturing steps and it reduces the overall efficiency of the continuous process.
Finally, the ethylene oxide polymer powder must be admixed in the desired ratio with a water-activated adhesive powder such as sodium alginate, when that embodiment is employed. Typically, a ribbon mixer is so utilized. Additional equipment: and personnel are required to monitor this solids mixing operation to prevent similar problems with agglomerate formation and dust formation.